This research project is concerned with the metabolic and ecologic interrelationships between oral microorganisms and salivary proteins. Its purpose is to extend earlier observations suggesting that organisms, such as Streptococcus mutans and Streptococcus sanguis, can obtain amino acids required for growth by attacking specific salivary proteins. This evidence was based on non-definitive criteria, namely, changes in the electrophoretic profile of saliva proteins following growth, and concomitant disappearance of amino acids from the total saliva protein concentrate. In order to substantiate these findings it is now proposed: (1) to isolate and characterize specific saliva proteins thought to be susceptible to attack by oral streptococci, (2) to isolate and characterize the microbial proteolytic enzymes involved, and (3) to test the puified protein both as substrates for growth of the streptococci and as substrates for proteolytic enzymes isolated from these organisms. It is further proposed to study the distribution of proteins in the individual salivary gland secretions, from caries-active and caries-free individuals, which are susceptible to proteolytic attack by specific oral streptococci. It is expected that these investigations in a previously unexplored area of dental research will provide new information on host associated factors which influence oral microbial ecology in general, and that this information may also be applicable to the specific problem of individual resistance or susceptiblity to dental caries in humans.